Lately the inkjet recording method is increasingly used in the production of large-scale outdoor advertisements, etc., requiring a large image area. For the base materials of these advertisements, etc., polyvinyl chloride sheets that are tough enough to withstand outdoor use, such as pure polyvinyl chloride resin sheets, tarpaulin sheets made of composite materials, and the like, are used. And, light-curable inkjet printing ink compositions free from volatile components are proposed as inkjet printing inks used for printing on these polyvinyl chloride sheets.
To make the aforementioned outdoor advertisements, etc., weather-resistant, not only the base material, but also the ink compositions, must be able to form a tough film. However, light-curable materials capable of forming a tough film tend to exhibit a lower adhesion to the base material because the film is generally very hard. Accordingly, a method of using an ink that contains, in part, a component to dissolve the base material is adopted to improve the adhesion of these ink compositions to the base material. For example, an active-energy beam-curable inkjet ink for polyvinyl chloride sheet, which contains, at a specific ratio, an ethylenic double bond-containing compound that does not dissolve polyvinyl chloride, and an ethylenic double bond-containing compound that dissolves polyvinyl chloride (N-vinyl caprolactam), is proposed (refer to Patent Literature 1).
However, a printed matter manufactured using such inkjet ink presents a problem in that, although the ink adheres well to the polyvinyl chloride sheet, cockling (phenomenon of the base material deflecting) occurs easily.
Also, use of a metal halide lamp or other traditionally and commonly used high-energy light source to cure images presents such problems as production of ozone, increase in the size of the irradiation equipment, shortening of the service life of the lamp, and the like. For these reasons, low-energy light-emitting diode (LED) lamps are used as light sources in recent years. This gives rise to requirements for curability, printability (adhesion, improvement of cockling, etc.) and safety (flash point, irritability, etc.) under low-energy LED lamps, and therefore light-curable inkjet printing ink compositions that can meet these requirements are proposed.
Among these light-curable inkjet printing ink compositions proposed are, for example, a light-curable inkjet printing ink composition that contains a pigment, benzyl acrylate, N-vinyl caprolactam, acrylated amine compound having two light-polymerizable function groups in the molecule and two amino groups in the molecule, and sensitizer (refer to Patent Literature 2), and a light-curable inkjet printing ink composition that contains a pigment, a compound containing (meth)acrylate and vinyl ether groups in a specific quantity of molecules, and a specific quantity of vinyl caprolactam (refer to Patent Literature 3).
However, these methods use a polyfunctional polymerizable compound in a large quantity and therefore produce a hard coating film of ink that tends to adhere poorly to the printing base material.